We have examined the absolute yield of keV x-rays emitted from gaseous plasmas created by the intense irradiation of large Xe clusters, We find that >10 mu J of x rays with photon energies above 1 keV are produced from clustering Xe gas targets when heated by 250 mJ, 2 ps laser pulses at an intensity of similar to 10(17) W/cm(2). The yields show strong laser intensity dependence and variation with Xe cluster size. (C) 1997 American Institute of Physics.